This module introduces batteries and describes the types of cells used, circuit arrangements, and associated hazards. How batteries are made, How to properly apply batteries. It contains the following topics: Battery Terminology (Voltaic Cell, Battery, Electrode, Electrolyte, Specific Gravity, and Ampere-Hour), Battery Theory (Batteries, Discharge and Charging of Lead-Acid Battery), Battery Operations (Series Cells, Parallel Cells, Primary Cell, Secondary Cells, Capacity, Internal Resistance, Shelf Life, Charge and Discharge), Types of Batteries (Wet and Dry Cells, Carbon-Zinc Cell, Alkaline Cell, Nickel-Cadmium Cell, Edison Cell, and Mercury Cell), and Battery Hazards (Shorted Cell, Gas Generation, and Battery Temperature).